The practice of ellipsometry requires that a beam of electromagnetic radiation impinge on a sample surface at a known oblique angle-of-incidence thereto. Where a sample surface is smooth it is generally not difficult to orient said sample so that the surface thereof generally faces in a know direction, thereby enabling the relatively easy orienting of the beam with respect thereto. This can be accomplished, for instance, by aligning a sample so that a typically collimated beam of electromagnetic radiation reflects directly 180 degrees therefrom using known technology, and then rotating said beam a known number of degrees. Where a sample surface is not smooth, however, irregularities thereof affect the actual angle, and plane of incidence of a fixed direction beam which is achieved from point to point thereon. It is also noted that unlike where a normal incidence beam is used, correlation between sample tilt and sample height can occur when a beam approaches the surface of a sample at an oblique angle. It should therefore be appreciated where a sample surface is not smooth, it becomes important to be able to identify, (preferably using a beam applied along a normal incidence), and correct for sample surface irregularities at a location thereupon which is being investigated.
A known approach to accomplishing point to point corrections of an angle-of-incidence involves placing a sample onto a stage which allows “X”, “Y” and “Z” translation capability as well as rotation capability around “X” and “Y axes and making adjustments to the orientation of a sample while directing a beam of electromagentic radiation downward, (as said system is viewed in elevation), onto a reflective objective located vertically above said sample so that said beam is caused to reflect therefrom over 360 degrees to a spherical mirror, onto a location on a sample to be investigated. Also present under said convex mirror is a prism which serves to direct an interrogation beam of electromagnetic radiation which approaches from the side, downward to the same spot on said sample being investigated. When said interrogation beam is caused to be reflected from the surface of the sample directly back through said prism, along the incident trajectory, it is determined that the sample surface at the point at which the interrogation beam interacts therewith is facing upward. While clever, it is noted that reflective optics are typically more expensive than refractive objectives and have a fixed focal length. On the other hand, refractive objectives with easily adjustable focal lengths, (ie. zoom lenses), are readily available and allow varying the viewing area of a sample.
While a specific Search was not conducted, known Patents are disclosed to aid the Examination:                Patent to Coates U.S. Pat. No. 4,373,817;        Patent to Coates U.S. Pat. No. 5,045,704;        RE. 34,783 to Coates;        Patent to Mikkelsen et al., U.S. Pat. No. 6,600,560;        Patent to Fanton et al., U.S. Pat. No. 5,596,411;        Patent to Piwonka-Corle et al., U.S. Pat. No. 5,910,842;        Patent to Piwonka-Corle et al., U.S. Pat. No. 5,608,526;        Patent to Bareket, U.S. Pat. No. 5,889,593;        Patent to Norton et al., U.S. Pat. No. 5,486,701;        Patent to Aspnes et al., U.S. Pat. No. 5,900,939;        PCT Application Publication WO 99/45340;        Published Application of Stehle et al., No. US2002/0024668 A1;        
A need for a system which accomplishes point to point sample surface orientation and which also enables observing the sample surface generally from above, at various user adjustable magnifications, is thus identified.